feat: add account management, email verification, AI fixes, and user guides

- Profile settings, account transfer, delete/leave account flows
- Email verification with JWT tokens and Resend integration
- AI assistant/copilot fixes: markdown rendering, shared RAG helpers,
  token tracking, input refocus, model_validate usage
- User guides hub + detail pages with 13 topic guides
- Sidebar and top bar navigation for guides

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/copilot.py

@@ -10,6 +10,7 @@ from typing import Annotated
 from uuid import UUID
 
 from fastapi import APIRouter, Depends, HTTPException, Request, status
+from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.rate_limit import limiter
@@ -25,6 +26,7 @@ from app.schemas.copilot import (
     CopilotConversationResponse,
     SuggestedFlow,
 )
+from app.models.copilot_conversation import CopilotConversation
 from app.services import copilot_service
 
 logger = logging.getLogger(__name__)
@@ -112,7 +114,7 @@ async def post_message(
     plan = await get_user_plan(current_user.account_id, db)
 
     try:
-        ai_content, suggested_flows = await copilot_service.send_message(
+        ai_content, suggested_flows, conversation = await copilot_service.send_message(
             conversation_id=conversation_id,
             user_id=current_user.id,
             message=data.message,
@@ -150,9 +152,12 @@ async def post_message(
         conversation_id=None,
         generation_type="copilot_message",
         tier=plan,
-        input_tokens=0,
-        output_tokens=0,
-        estimated_cost=0,
+        input_tokens=conversation.total_input_tokens,
+        output_tokens=conversation.total_output_tokens,
+        estimated_cost=(
+            conversation.total_input_tokens * 1.0 / 1_000_000
+            + conversation.total_output_tokens * 5.0 / 1_000_000
+        ),
         succeeded=True,
         counts_toward_quota=False,
         error_code=None,
@@ -163,7 +168,7 @@ async def post_message(
 
     return CopilotMessageResponse(
         content=ai_content,
-        suggested_flows=[SuggestedFlow(**sf) for sf in suggested_flows],
+        suggested_flows=[SuggestedFlow.model_validate(sf) for sf in suggested_flows],
     )
 
 
@@ -174,9 +179,6 @@ async def get_conversation(
     db: Annotated[AsyncSession, Depends(get_db)],
 ):
     """Get copilot conversation history."""
-    from sqlalchemy import select
-    from app.models.copilot_conversation import CopilotConversation
-
     result = await db.execute(
         select(CopilotConversation).where(
             CopilotConversation.id == conversation_id,